Collaborations with Sanaria Inc and the Malaria Research and Training Center at the University of Bamako, Mali to conduct these PfSPZ related studies was initiated in 2012. PfSPZ Vaccine in Mali (NIAID Protocol 14-I-N010) Since January 2013, we have been preparing for a study to test the safety, immunogenicity and efficacy against naturally occurring malaria infection of PfSPZ Vaccine in Malian adults. The phase 1 double-blind, randomized, controlled trial to assess the safety, immunogenicity, and protective efficacy of repeated IV immunization with PfSPZ Vaccine in Mali started in January 2014 in Doneguebougou, Mali at the Malaria Research and Training Center with complete enrollment into the study by February 2014. Twelve subjects were initially enrolled in a staggered manner for safety in the pilot safety group and received their first vaccination (1.35x105 PfSPZ Vaccine) the week of 28 January 2014, and then received 2.7x105 PfSPZ Vaccine two weeks later. 97 subjects were initially enrolled of which 96 subjects were stratified by village and randomized for the main group. Of those 96 subjects, 93 subjects (46 PfSPZ Vaccine; 47 placebo) received their first vaccination starting the week of 24 February 2014. The final vaccinations were received by 88 subjects (44 PfSPZ Vaccine; 44 placebo) the week of 14 July 2014. The primary efficacy endpoint of the study started the week of 11 August 2014 (28 days following receipt of the fifth vaccination) and the final study visit was completed on 05 January 2014. Of the 88 subjects in the main group who received all five vaccinations, 86 subjects (42 PfSPZ Vaccine; 44 placebo) completed the study through the transmission season to the last study visit 88 healthy malaria exposed Malian adults (44 PfSPZ Vaccine; 44 Placebo) received five doses of vaccine and 86 (42 PfSPZ Vaccine; 44 Placebo) were followed actively every two weeks for up to 24 weeks post vaccination #5. PfSPZ Vaccine was easy to administer, and was safe and well tolerated. P. falciparum infections 28 days post vaccination 5 occurred significantly earlier in the control group than the PfSPZ Vaccine group. PfSPZ Vaccine is safe, well tolerated, and is the first vaccine to show evidence of sterile protection to African adults from natural P. falciparum infection over the course of an entire malaria season. PfSPZ Vaccine in Mali, Africa Dose Escalation (16-I-N004) Our initial results from Protocol 14-I-N010 have been encouraging given the following: 1) the protective efficacy was significantly higher than has ever been demonstrated by immunization with a malaria vaccine in adult Africans, 2) the PfSPZ Vaccine was efficacious against heterogeneous African P. falciparum parasites and 3) there was no evidence of waning of immunity during the 6 month follow up period. In addition, all doses were safe and well tolerated with little reactogenicity or adverse events reported. On the other hand, protection in both Tanzania and efficacy in Mali were lower than what was recorded in the USA, and it does not meet our expectations for a licensed PfSPZ Vaccine. One possible explanation for the lower rates of efficacy was provided by our assessment of antibody responses seen in Mali and Tanzania as noted above. These results clearly demonstrate that healthy Tanzanian and Malian adults do not produce comparable antibody responses to PfCSP after immunization with PfSPZ Vaccine to the non-Pf malaria-exposed adults in the U.S. Because adults play a significant role in transmission of P falciparum, and if PfSPZ Vaccine is to be used as a tool for elimination, it must be protective in adults. We think that the most likely explanation for the poor immunogenicity and protection in the adult Africans is immunoregulation due to lifelong exposure to P falciparum infections. Thus, we hypothesize that we can improve efficacy by increasing the number of PfSPZ Vaccine per dose, increasing the interval between the first and second doses to 8 weeks (as was done in WRAIR 2080 in the group receiving 3 doses of 4.5x105 PfSPZ), and reducing the number of doses to three. Additionally, we hypothesize that we can learn how the standard CHMI model may be used in the field and start to explore the impact such factors as malaria co-infection and drug treatment have on vaccine responses. PfSPZ CVac-PYR (NIAID Protocol 15-I-0169) As previously noted, a human study suggested that anti-infection immunity might be achieved with a much smaller parasite inoculum. This method of immunization by experimental P. falciparum infection in conjunction with antimalarial prophylaxis is referred to as chemoprophylaxis with sporozoites (CPS), infection treatment vaccine (ITV), and chemoprophylaxis with sporozoites (CVac) by different authors. We use the term CVac in this Protocol to refer to this vaccine concept. Since chloroquine is a blood-stage schizonticide, the degree to which the protective immune response induced by the chloroquine CVac model targets liver or blood-stage antigens is unclear from the study of Roestenberg et al. Further, limited data in both animal and humans indicate that exposure to blood-stage parasites may abrogate liver-stage immune responses. It is important to further define whether sterile protective immunity to P. falciparum can be induced by wild-type (non-attenuated) sporozoite immunizations when exposure is limited to sporozoite and pre-erythrocytic stages of the parasite life cycle and by a low dose of sporozoite inoculum. This study will evaluate a CVac regimen using chloroquine weekly in addition to pyrimethamine. This combination will attempt to prevent the development asexual erythrocytic stages of the malaria parasite. By completely preventing the release of blood-stage parasites, this CVac regimen will extend the findings of Roestenberg et al. and explore whether highly protective anti-infection immunity and sterile protection from homologous P. falciparum challenge can be induced by exposure that is limited to the liver-stage of parasite development. Exploration of stage-specific immune responses involved in protective immunity to P. falciparum and discovery of new target antigens is critical for future development of malaria vaccine strategies. The intervention in this study is induction of stage specific immunity (pre-erythrocytic immunity) to malaria following direct venous inoculation (DVI) with aseptic, purified, vialed, cryopreserved, fully infectious NF54 PfSPZ (referred to as Sanaria PfSPZ Challenge) produced by Sanaria, Inc when exposure is limited to the SPZ and liver-stages of the parasite life cycle and at a low dose PfSPZ inoculum (51,200 Sanaria PfSPZ Challenge) via the following regimens: PfSPZ Challenge under chloroquine coverage or PfSPZ Challenge under chloroquine and pyrimethamine coverage for a total of 3 exposures while subjects are under one or two malaria prophylaxis regimens listed above. Protective efficacy will be assessed by homologous CHMI via PfSPZ Challenge via DVI.